Method for controlling a CNC machine tool

ABSTRACT

The invention relates to a control system of a CNC machine tool with cyclically recurring sequences. The control system has a data input and visualization unit, a machine check unit and a NC control unit with at least one stored NC program for generating movement sequences for the CNC machine. Functional data which are required for the machining of a specific work piece and which have been fed into the data input and visualization unit or selected in the unit are conveyed from the data input and visualization to the NC control unit. The machine check unit calls up function modules of the NC control program according to selected control data and by means of control codes, said function modules representing part programs, and proceeds from one function module to the next independently of its hierarchical position in the tree structure. In so doing, the machine check unit deactivates the hold commands in each function module by means of the control codes. The machine check unit takes into account the transition functions between individual function modules when switching from one function module unit to the next. The transition functions are necessary for physically initializing or loading the data for the CNC machine tool.

The present invention relates to a method for controlling a CNC machinetool, which has cyclically recurring sequences, according to thepreamble of patent claim 1 as well as to a control system for a CNCmachine, according to the preamble of patent claim 6.

Under control systems one understands the combination of mechanics,electronics and information technology, which in automatisationtechnology permits a working procedure to automatically take its courseaccording to a predetermined program.

Todays state of such control systems is for example described in thetextbook of Manfred Weck, “Werkzeugmaschinen, Fertigungssysteme”, Volume3.1, VDI publishing house Duesseldorf, 1995 as well as in Dubbel,“Taschenbuch für den Maschinenbau”, 17th edition, Springer publishinghouse, Berlin 1995.

Generally the control system today is subdivided into three levels orunits:

a data input and visualisation unit, also called a man-machine interface(MMI) which permits or makes available the machine and operating dataacquisition, the choice of the machine mode to be carried out, the orderadministration and the process visualisation,

an adaption control unit acting as a central control unit, also called aSPS or PLC (programmable logic controller), with a control program whichaccording to the state of the art obtains the entirety of directions andagreements for the signal processing,

an NC control unit (NC=numeric control), in which function sequences inNC control programs are stored. These NC control programs containgeometric data concerning the path information, technological data suchas cutting speed, advance, spindle rotational speed, as well as altercommands, such as tool exchange, the equipping and removal of parts.Recurring movement sequences are filed several times in the NC programin accordance with the recurrence.

Data inputted via the MMI unit for defining the subject to bemanufactured are decoded in the NC control unit and are processedfurther separately according to geometric, technological data and switchcommands. Switch commands are transmitted further to the SPS controlunit, where they are linked to feedbacks of the machine tool and inaccordance with the control program processed step by step, areconverted into control commands which synchronise the membered NCprogram. Geometric and technological data, after the calling-up by wayof the NC control unit, produce corresponding axes movement commands forthe machine. NC units and SPS units for the puprose of processvisualisation inform the actual machine status to the MMI unit.

An important demand of such control systems is that they must be asflexible as possible, so that changes in the mechanics of the CNCmachine or in the input mask of the MMI do not require a complete newprogramming of the machine.

In order to permit an extension of the mechanics of the machine tool,thus the control system disclosed in EP-A-0 553 621 from the start hasat its disposal at least two SPS modules, wherein the first SPS moduleassumes the machine control and the second SPS module is present as areserve. In the case of a machine extension only the second SPS moduleneeds to be provided with the new machine functions for the furthermachine movements which are coupled automatically to the first SPSmodule by the control system. A renewed programming or a replacement ofthe already present, programmed first SPS module is not necessary.

In EP-A-0 642 066 there is set the object of flexibilising the dialogueguidance, so that the man-machine interface (MMI) may be adapted to theamended requirements of the user in a simple way and manner. Adialogue-orientated programming system for producing control programshas at its disposal a data forwards-backwards access unit whichseparates each program set up in a programming system into the partcontrol data “machine control data” and “dialogue control data” whichare provided with linkage keys. The machine control data are depositedinto a machine program memory and the dialogue control data into abackground memory. Via the logic keys they may again be constituted intoa control program and filed in the background memory.

The control systems of CNC machines according to the state of the artare generally designed to be able to control as many as possible and asvaried as possible machine movements, so that they attempt to form theindeed rigid central control unit more flexible with their SPS modules.This however leads to complex control systems, which as previously mayonly be changed by qualified specialists.

There are however also machine tools which have a noticable cycliccharacteristic. One example of such a type of machine tool is agearwheel grinding machine. The movements which a machine with a cycledcharacteristic are to carry out are repeated cyclically. Furthermore forall subjects the same subject shapes are used. The differences in thecontrol system which lead to differently shaped subjects lie only in theoperating parameters or control data, not in the basic movementsequences which are defined by individual machining functions.Furthermore the sequences and the hierarchies of the individualmachining functions are unambiguously fixed and do not change. Themachining functions for themselves as well as their hierarchy amongstone another even with an extension or modification of the machine alwaysremain the same, so that the SPS module of the central control unitaccordingly must always transmit the same control commands to the CNClevel.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a method for thecontrol of such a CNC machine with a noticeable cyclic characteristic,in particular of a gearwheel grinding machine, as well as to provide acontrol system, which permit a simple changing of programs and by way ofthis a high flexibilisation.

This object is achieved by a method with the features of the patentclaim 1 as well as a control system with the features of patent claim 6.

The invention is based in the recognition that with machines withcyclically recurring sequences the function control of the machinewithin the sequence does not change and thus the master-slave principlemay be used. By way of this the hierarchies between the central controlunit and the NC control unit may be fixed more unambiguously than withthe known CNC control systems.

According to the invention the NC program consists of several partprograms or function modules which contain individual machiningfunctions and which in each case are provided with an automaticallyexecuted hold command. The individual function modules may be called upby way of control codes of the machine control unit, whereinindependently of their hierarchical position in the NC program one maychange from one function module into the next. The control codes are setby the MMI unit in a context-sensitive manner.

According to the invention data inputted via the MMI unit is separatedinto function data for the machining functions and into control data forthe choice of the function modules, wherein the former is transfered tothe NC control unit where in accordance with the NC control unit it isused in this. The control data is transfered to the machine control unitwhere in the form of control codes or target codes in a central controlprogram they serve the selection of the function modules of the NCprogram.

This machine control unit replaces the known SPS control unit, since itassumes all exercises of the known SPS control unit. It is furthermorein the position of determining which function module should be runthrough next and thus assumes to a greater extent the effective controlof the CNC machine. With this it fixes the path to be gone throughwithin the program tree from the last activated function module to thenew destination of the NC program, wherein the NC program may be runthrough in any direction. Thus not only does a hierarchical processingtake place but also cycles interconnected within each other, a change toequal levels or jumping back to hierarchal higher planes are possiblethanks to the machine control unit which by way of transition functionscontained in the NC program, the physical preparation of the machine forcarrying out the next machining function is ensured.

Since the individual function modules during a single sequence of the NCprogram may be called up several times, each processing function onlyneeds to be carried out once in the NC program. The NC program accordingto the invention is thus simply constructed and does not unnecessarilyrequire memory space.

According to the invention the function modules or menu points of an NCprogram are grouped together to a program tree. Which branch of theprogram tree is run through is determined by the machine control unit.Since it knows the linkage structure in the program tree it isfurthermore in the position of determining the path from one branch tothe next. Generally a single NC program is sufficient, the integrationof several NC programs in a single NC control unit is however possible.

Thanks to the cooperation, according to the invention, of the MMI unit,the machine control unit and the NC unit, an existing control system maybe changed or supplemented in a simple way and manner. If new machiningfunctions are to be introduced, the integration of a new function modulein the program tree as well as the placing of a new control code in theMMI unit are sufficient, these being transmitted to the machine controlunit. If existing machining functions are to be provided with newcontrol data then their placing in the MMI unit is sufficient. The usermay thus carry out supplements and changes without having to change thecentral control program of the machine control unit. Examples for thisare, a change of the data necessary for carrying out the machiningprocedures, the addition of new data, for example for a new machiningtool or for a gearwheel with new dimensions or for carrying out new axismovements. With the changing or supplementing of the control thus notall of the interrelationships must be recognised since the treestructure of the NC program avoids false movements of the machine tool.The use of two primary files which may be copied in any manner, one forthe control data and another for the function data, permit a quick andreliable addition of new control elements. Above all in the region ofthe MMI unit the change may be carried out without compiling by way ofpure ASCII editing procedures.

Furthermore the MMI unit, in particular an operation and selectionsurface may be formed flexible and be changed in a simple way and mannerwithout having to entail a change of the machine control unit.

Furthermore it is advantageous that by way of the control, according tothe invention, of the NC program the danger of program call-ups leadingto undesired interruptions of the subject machining procedure isavoided.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings the control system according to theinvention is shown schematically and in the subsequent descriptiontogether with the method according to the invention is described in moredetail. There are shown:

FIG. 1 a schematic representation of the units of the control systemwith a simplified detail of the data flow;

FIG. 2 a schematic representation of the data blocks in the MMI unit;

FIG. 3 a schematic representation of a program tree and

FIG. 4 a schematic representation of a function module.

DETAILED DESCRIPTION

In FIG. 1 there is shown simplified the control system according to theinvention for a gearwheel grinding machine, wherein auxiliary functioncontrols and control mechanisms and enquiries which are not essential tothe invention are not drawn in.

The control system consists essentially of three units: of a data inputand visualisation unit, also called MMI unit 1, of a central controlunit or machine control unit 2, and of a NC control unit 3.

The MMI unit 1 makes available to the user an operating and selectionsurface, in order to select or input operating parameters (control data10) and machine mode (function data 11). This operating and selectionsurface may be formed in the form of a matrix (matrix-select-guide) oras is shown in FIG. 1, correspond to a tree (tree-select-guide). Thistree may, but not necessarily, correspond at least approximately to theNC program structure. Preferably in the same MMI unit the matrix as wellas the tree are offered, wherein the user in each step of the operatingand selection surface may change from one variant to the next.

The MMI unit 1 contains at least two primary files, wherein a firstprimary file contains all method-characteristic data necessary for thecomplete NC functionality and a second primary file contains all datanecessary for the data input. From both primary files any number ofcopies may be produced and each file may be edited for itself. To thefirst primary file there are linked the function data 10 necessary forthe specific machining of a subject, to the second primary file there islinked the control data 11 defining the machining functions.

The function data 10 are preferably grouped together in data blocks 10′as this is schematically shown in FIG. 1. Each data block 10′ comprisesa part region of the CNC machine, for example as is shown in FIG. 2there are present data blocks for the machine data, for tools to be usedsuch as dressers or grinding disks, and for subjects to be manufacturedsuch as gearwheels. The user selects from from existing, already storeddata blocks or from generated data blocks with new details, for examplefor an additional gearwheel. Newly inputted data are subjected to aplausibility check.

The control data 11 serves the carrying out of various machine modes,such as profiling, grinding and diameter turning, wherein generally onemay select between a mode for setting up the machine, a manualoperation, a semi-automatic or an automatic operation. The control data11 itself directly forms the control code necessary for the control ofthe NC program tree or may be unambiguously transmitted into this code.

The machine control unit 2 according to FIG. 1 consists of at least one,preferably several control modules 20 which in their function activationare constructed preferably hierarchical. For example an upper controlmodule controls user sequences, the next lower control module concernsthe periphery agreement and a next is responsible for the driver.

In the NC unit 3 there is stored at least one NC control program 30 forgenerating the machine movements. The NC control program 30 ispreferably formed in the form of an NC program. It may however be formedby any type of non-interpretive program of the NC unit. The NC controlprogram 30 comprises a tree structure which is described further belowby way of FIGS. 3 and 4.

After the user in the MMI unit 1 has inputted or selected the functiondata 10 as well as the control data 11 for a specific machiningprocedure, the selected function data 10 is directly led (13) to the NCcontrol unit 3 and the control data 11 transfered (12) to the machinecontrol unit 2.

The control data 11 activate in the machine control unit 2 a centralcontrol program which in steps and in a cyclic succession passes on (23)control codes to the NC control unit 2. The control codes activate viacode addresses individual function modules, of the NC unit 3, which arein active connection with the drive of the CNC machine and whichactivate the drives of the CNC machine. The NC control unit 3furthermore before, during and after the machining process, with meansnot shown here, checks the machine status and leads this further (32) tothe MMI unit 1 directly or via the machine control unit 2.

In FIG. 3 there is represented an NC program according to the inventionin the form of a program tree. The uppermost branching-out of the treedifferentiates the basic modes 31 of the gearwheel grinding machine,specifically the setting up, manual, part automatic and automaticoperation. These basic modes may be separated also into separate NCprograms. Each mode branches out in further planes which relate tocertain machining types 31′, such as dressing, equipping, grinding ormeasuring. At least one part of the machining types 31′ in turn branchesout into individual machining sub-types 33 such as diameter turning orprofiling which via one or several further branching-outs end in theeffective machine control commands 34. In the branching-outs there arepresent at least partly transition function modules TF. Such transitionfunctions are for example procedure movements, trigonometric functions,algorithms, dialogues or switch functions.

Each level of the program tree 30 is essentially constructed identicallyand consists of one or more part programs or function modules 35. Such afunction module 35 is shown in FIG. 4. It consists of a preparation part36 and a subsequent execution part 37. At the beginning of thepreparation part 36 there is a hold command H. Subsequently therefollows a back-distributer V1 which selectively leads to the next higherlevel or hierarchically leads up to the function preparation FV.Subsequently there follows a function back-distributer V2 which in thecase of an error notice E1 leads into the next higher level. Otherwisewithin the function module it is transmitted further into the executionpart 37 where via a function distributor V3 a machining function F iscalled up, for example an axis movement from a point X to a point Y.After the execution of this function in the case of an error notice E2there is effected a feedback via a function back-distributor V4 to theupper level. Otherwise the function back-distributor V4 initiates aretro-machining function FN, for example a lifting of a machining toolfrom the subject. The retro-machining function FN after completionreturns to the hold command H.

Each function module 35 or its hold command H is provided with anidentification number, also called target code. This target code ispreferably selected such that each plane has at its disposal a numberset and number sets of the next higher levels prefix this number set.For example the function “profiling” shown in FIG. 3 is provided withthe target code “112”. This target code in accordance with the userinput in the MMI unit 1 via the machine control unit 2 is selected viathe control code, the hold command is deactivated and the correspondingfunction module 35 is carried out. The target code and the control codeare preferably identical.

The starting of such a function module 35 by way of a control code maybe understood by the man skilled in the art and is therefore notdescribed in detail in the following. Particular on the other hand isthe changing from a function module 35 into another further module. Thisis effected after the selection of the target code via the MMI unit byway of a state machine which is integrated in the machine control unitand which is organised as a step chain, thus an NC dialog-capableautomatic machine which recognises the linkage structure of the programtree. The machine control unit thus decides on account of the treestructure which transition functions TF must be necessarily carried outin order to physically convey the machine tool from the momentaryposition in the program tree up to the new start position for the newfunction module to be carried out. The transition function TF thusensures that the machining tools are traversed to the desired positionand the machine is prepared for carrying out the next operating functionor ensures that the dialogues or computations necessary for the nextaction are carried out and the necessary data is prepared.

The transition functions may, as shown in the Figures, lie between theindividual function modules. In other variants the transition functionsare integrated in the function modules, for example in that they areintegrated in the function preparation FV. Likewise it is possible thatin a function module there are several function preparations FV as wellas several retro-machining functions FN. For example a functionpreparation FV is arranged in front of the halt command and onesubsequently after the halt command. In the same manner a firstretro-machining function is run through in the case that the module isnot left and a second retro-machining function in the case that themodule is left.

We claim:
 1. A method for controlling a CNC machine tool which hascyclically recurring sequences, in particular of a gearwheel grindingmachine, with a data input and visualisation unit, with a machinecontrol unit and with a NC control unit with at least one stored NCcontrol program for generating movement commands for the CNC machine,wherein in the data input and visualisation unit selected control datadefining machine modes are led further to the machine control unit, andwherein function data which is inputted into the data input andvisualisation unit or is selected in this, and which is necessary forthe machining of a specific subject, is led from the data input andvisualisation unit to the NC control unit, characterised in that themachine control unit in accordance with selected control data by way ofcontrol codes calls up function modules, of the NC control program,representing part programs, and independently of their hierarchicalposition in the NC control program leads them from one function moduleto the next, wherein by way of the control codes hold commands (H)present in each function module are deactivated and wherein the machinecontrol unit on changing from one function module to the next takes intoaccount transition functions (TF) for the physical preparation and/ordata preparation of the CNC machine tool.
 2. A method according to claim1, characterised in that after processing a function module oneinitialises a hold command (H) present at the beginning of each functionmodule.
 3. A method according to claim 2, characterised in that afterprocessing a function module before initialising the hold command (H) aretro-machining function (FN) is called up.
 4. A method according toclaim 1, characterised in that in an activated function module at leastone further function module interconnected therein is called up.
 5. Amethod according to claim 1, characterised in that the function data isstored in the data input and visualisation unit by copying a firstprimary file and the control data by copying a second primary file.
 6. Acontrol system for a CNC machine tool which has cyclically recurringsequences, in particular for a gearwheel grinding machine, with a datainput and visualisation unit for inputting or the selection of functiondata necessary for the machining of a specific subject and the controldata defining the machine mode, with a machine control unit forcontrolling the CNC machine tool and with an NC control unit with atleast one stored NC program for generating movement commands for the CNCmachine, characterised in that the at least one NC program comprises atree structure which is formed by several function modules representingpart programs, that each function module is provided with a hold command(H) which in accordance with selected function data is deactivatable byway of control codes transmittable from the machine control unit, thateach function module independently of its position in the tree structurecan be called up by the machine control unit and that in the NC programbetween the function modules there are present at least partlytransition functions (TF) for the physical preparation and/or datapreparation of the CNC machine tool.
 7. A control system according toclaim 6, characterised in that the function modules have an identicalstructure.
 8. A control system according to claim 7, characterised inthat the hold command (H) is arranged at the beginning of the functionmodule and that a loop from the end of the function module leads backinto the hold command (H).
 9. A control system according to claim 6,characterised in that on one branch of the tree structure there arepresent several function modules.
 10. A control system according toclaim 6, characterised in that the function data can be stored in copiesof a first primary file and the control data in copies of a secondprimary file.
 11. A control system according to claim 10, characterisedin that the primary files have an ASCII format.